-LRB- CNN -RRB- -- A fast-developing storm spawned at least one tornado Sunday in Billings , Montana , ripping the roof off a massive entertainment complex and causing extensive damage in the region .

No injuries were reported .

Amateur video shows the funnel cloud hovering over the MetraPark venue -- home to a sports arena , expo center and other facilities -- kicking up debris and peeling away the roof of one of the complex 's buildings .

Gov. Brian Schweitzer estimated that the roof damage could cost between $ 8 million and $ 15 million , but noted it was fortunate the arena was not hosting an event when the twister struck around 4:30 p.m. -LRB- 6:30 p.m. ET -RRB- .

The damaged building held a football game at the same time just a night earlier , he said .

Meteorologist Keith Meier of the National Weather Service in Billings estimated the tornado to be as strong as an EF2 on the Enhanced Fujita scale , with winds estimated at more than 100 mph .

Meier said the storm also produced quarter - to half-dollar-sized hail .

Schweitzer plans to travel to the region Monday to survey the damage ; he said the National Guard is ready to assist in cleanup efforts if needed .

CNN 's Jessica Jordan and Justin Lear contributed to this report .

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No injuries reported from fast-developing storm

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Roof damage to MetraPark venue estimated to be as high $ 15 million

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Governor to tour affected region Monday